Invasive insect called ‘imminent threat’ to state agriculture, economy

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An infestation of the peach fruit fly has been found in parts of East
County after four of these insects were trapped in Oakley and Brentwood.
(Courtesy Curtis Takahashi/California Department of Food and Agriculture)

EAST CONTRA COSTA COUNTY — Crews will begin treating areas of Oakley, Brentwood and Antioch to eradicate invasive peach fruit flies after four were recently discovered, posing what officials call “a statewide imminent danger to the environment and the economy.”

Karen Ross, the secretary of California’s Department of Food and Agriculture, said in a website notice Thursday that authorities have determined from weeks of trapping and surveys that a breeding population and infestation of peach fruit flies exists in parts of East Contra Costa County.

The flies were trapped between July 31 and Aug. 14 in residential neighborhoods in Oakley and Brentwood, according to a notice posted on the Department Food and Agriculture website and emailed to government officials Thursday night. The peach fruit fly is considered “a devastating pest of a wide variety of important fruit and vegetables,” including peaches, pears, apples, apricots, citrus, tomatoes, cucumbers, watermelons, figs, dates and avocados, according to the department.

State officials said that after original trappings detected fruit flies in peach, apple and fig trees, additional surveys were done to determine the extent of the infestation and the area that needs treatment. Based on those results and recommendations from Contra Costa County agricultural commission representatives, it was decided that chemical treatment and possibly host fruit removal would be the best ways to eradicate the peach fruit fly, according to the notice.

Treatment will begin Saturday, said Jennifer Gordon of the California Department of Food and Agriculture’s Pest Detection/ Emergency Projects.

“It (East Contra Costa County) is not a normal spot for us to get them — that’s why we wanted to jump on it right away,” she said. “If we get it early enough, we don’t normally find any more.”

JJ Sohal, the department’s senior environmental scientist, said field specialists will place up to 400 bait stations over the next three days in the approximately 19-square-mile affected area. The baits, which contain the organic pesticide Spinosad, are meant to attract male peach fruit flies by mimicking the females. The flies are killed when they ingest the insecticides, she said.

Applications will be repeated every two weeks throughout the flies’ life cycles, which depend on temperatures, with warmer weather hastening the cycles, Sohal said. If East County temperatures remain high, the flies’ life cycles and treatment program will likely last about two months, she added.

“We’re trying to get all the males,” Sohal said. “We have traps for the females too, but they are different.”

The male-attractant approach has successfully eliminated dozens of fruit fly infestations in California, said Contra Costa County Agricultural Commissioner Matt Slattengren. Though fruit flies have been found in past years in other parts of the county, the commissioner said this is the first time in 20 years they have been discovered in East Contra Costa — only a mile from prime agricultural land. County officials plan to place dozens of additional traps in the four locations — three in Brentwood and one in Oakley, where the fruit flies were found — and check them frequently.

“It looks like we caught it early, but being that it is close to ‘ag’ areas, that’s why we are so concerned,” Slattengren said. “If we let this go, and this becomes established, every backyard fruit tree will be full of maggots and every grower will have to forever spray or they (the flies) will become established and destroy their crops.”

Peach fruit flies are native to much of mainland southern Asia and its neighboring islands and recently have invaded North Africa. They are known to attack more than 50 types of fruits and vegetables, officials say. Damage to the fruits occur when the female lays eggs inside and they hatch into larvae, which then tunnel through the fruit’s flesh, making it inedible, according to the California Department of Food and Agriculture. Officials say the exotic pests usually hitchhike on produce transported illegally from other countries.

Crews will begin treating areas of Oakley, Brentwood and Antioch to eradicate invasive peach fruit flies after four were recently discovered, threatening peach trees like this one above and posing what officials call “a statewide imminent danger to the environment and the economy.” (Judith Prieve/for Bay Area News Group)

In the East County case, the flies were detected as part of an ongoing coordinated pest prevention program in which county workers place and check traps to detect any harmful insects.

“We are concerned about it because we found four. We think there is an infestation, and we want to address it before it gets out of control,” Sohol said. “If untreated, it would be devastating to the fruits and crops.”

The peach fruit fly in California was first detected in 1984, in Los Angeles County. It was eradicated but has since been reintroduced multiple times, including most recently in Palo Alto in late June, prompting a treatment program in Santa Clara and San Mateo counties using organic insecticides.

Where fruit removal is required, residents will be notified in writing at least 48 hours in advance of any treatment, officials say. Residents who think they may have spotted a peach fruit fly or other harmful insect can call the CDFA Pest Hotline at 800-491-1899. Treatment information is posted at bayareane.ws/2KPOCnR.

Judith Prieve is an East Bay journalist. A graduate of the University of Wisconsin-Madison, she has worked as a reporter, features editor and assistant metro editor at newspapers in Wisconsin and Northern California and has been at what is now the Bay Area News Group for more than 25 years.

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